Process for the explosive pressing of powdered compositions



Aug. 11, 1953 D CO IONS Filed Aug. 6, 194'? P. M. MGKENNA ETAL I2,648,125 PROCESS FOR THE EXPLOSIVE PRESSING 0F POWDERE MPOSIT 3 Sheets-Sheet 2 IN VENTORS' PHILIP M. McKlENNA JOHN C. REDMOND fMLYN IV. ITH

Blf/@ ma HEIR ATTR NEYS Aug. 1'1, 1953 .MCKENNA E-rAL 2,648,125

PRESSING P. PROCESS THE EXPLOS OF POWDERED COMPO IONS Filed Aug. 6, 1947 5 SheetSPShee 5 FIG. 9 70 FIG. 1o 70 69 79 12 JNVENTORS PHILIP M. MCKENNA .T0/IN C. REDM OND MLY/Y M 'M/T I rf'm Arm/infer:

Patented ug. 1v1, 1.95.3

PROCESS FOR THE EXPLOSIVE PRESSING F POWDERED COMPOSITIONS Philip M. McKenna, Greensburg, and John C. p Redmond and Emlyn N. Smith, Latrobe, Pa., assignors to Kennametal Inc., Westmoreland County, Pa., a corporation of Pennsylvania Application August 6, 1947, Serial No. 766,570

3 Claims.

vThis invention relates to a process for the explosive pressing of powdered metal compositions, and more particularly pertains to such pressing carried on in a fluid medium.

In molding articles of powdered metals or of powdered metal compounds, or mixtures of them, particularly articles made of hard carbides, nitrides, and borides of various metals, with or without binder materials, and which articles are thereafter to be sintered to a firmly coherent or cemented condition, it is most desirable to achieve a dense, non-porous, and uniform compacting of the powdered material into an intermediary self sustaining shape before sintering.

Although the process is adapted for use in connection with the pressing of articles as described in McKennas United States Patent No. 2,220,018, issued on October 29, 1940, which discloses the use of a thin rubber bag to hold the particles in loose form and to define the molded form finally to be produced, it is also adapted to the nal compacting of pre-formed shapes made by a pre1 liminary low pressure molding operation. This novel process subjects such compositions to a compacting under explosive pressures of very high value, in a fluid, to the end that the thereby formed briquette or compact is made very dense and uniformly dense.

The uniformly dense condition of briquette articles or compacts made by the process herein described adds greatlyuto the strength of the article when sintered and assures that there will be a minimum of distortion and warping during sintering.

The uniform pressing in all directions upon the composition obtained by the application of explosive forces to a confined fluid medium containing it, results in the formation of an article in which there exists no strains, internally there` of, due to unequal directional forces acting thereon as occurs in pressing such compositions in a rigid mold or die.

In carrying out the process we utilize a fluidimpervious sheath of bag-like formation, into which is placed the powdered materials or preformed shape which is to be finally pressed to the explosively compacted condition, said bag being preferably made `of rubber or rubber-like material having elastomeric and fluid proof characteristics, so that, during the pressing operation, the composition will be protected from contact with or penetration by, the fluid of the medium in which the bag is placed prior to the explosion. The fluid is confined in a chamber to which explosive forces are applied. By use of (Cl. .Z9-160.5)

the process and device of this invention superior articles made of powdered metal or metal compounds may be repeatedly produced cheaply and quickly with uniform results.

In general, the device used in carrying out this process comprises a fluid-holding pressure chamber, of strength sucient to resist bursting from explosive forces applied internally thereof, the chamber having an opening to which may be coupled, in gas and fluid sealing fashion, an explosion head chamber which contains a piston to be driven therefrom, by an explosion, against the fluid held in thepressure chamber. Preliminarily the object or particles to be compacted, are placed in the sheath, which, preferably, is evacuated of air or gas, and are then placed in the pressure chamber, after which the chamber is lled with the fluid, such as water, to the brim. Then the explosion chamber head, first having been packed with an explosive, such as gun powder, has the piston placed thereagainst. This explosion head and piston then are coupled to the pressure chamber so the piston rests against the fluid, and the explosive charge is detonated. After a short interval of time, the gases of the explosion, having performed their work, are released from the explosion chamber by a special valve, the explosion chamber head and piston are removed from the pressure chamber and the nal compacted article is removed from the iiuid and enclosing sheath,

It has been found that articles so compacted have considerably greater and more uniform density than those compacted in any other manner heretofore known, have less warpage and less porosity in the finished product, after sintering, and have higher strength characteristics. For compacted and sintered articles requiring considerable strength, equalized in all directions, such as rolls, for instance, the process is of considerable value, in that the compacting pressure being directed, by the uid, from all sides, equally, gives a uniform condition of density and strength throughout the mass of each such article.

Therefore, it is an object of this invention to provide a process for compacting powdered metal, or powdered metal compositions, in a fluid medium to which compression forces are applied by an explosion.

Various other objects of the invention will become apparent from the following specification read in connection with the drawings in which:`

Fig. 1 is a sectional view through the device showing an article containing bag in the pressure chamber, in condition for an explosion,

3 Fig. 2 shows the substance of Fig. 1 after the explosion has occurred, some of the parts that were shown in Fig. 1 having been broken away and others being shown in elevation.

Fig. 3 is an elevation of the outside end of the v explosion head.

Fig. 4 is a section through the device on the line 4-4 of Fig. 1.

Figs. 5 and 6 are, respectively, an end elevation and a side elevation of the piston.

Fig. 7 is a detailed showing, partly in section, of the ignition device by which the explosive charge is detonated.

Fig. 8 is a view of that end of the ignition device of Fig. 7, which has the ring gap between the electrodes.

Fig. 9 is a detail of the explosion chamber relief valve, with certain parts broken away to show the interior.

Fig. 10 is a section through the explosion chamber relief valve shown in Fig. 9.

Fig. 11 is a detail of that portion of the relief valve of Figs. 9 and 10 which contains the needle valve seat.

Fig. 12 is a section through the substance of Figs. 9 and 10 on the line |2|2 of Fig. 10.

Fig. 13 is a detail of the central ignition electrode of the igniter shown in Fig. 7, with special reference to the insulation thereof.

Fig. 14 is a section on the line |4-I4 of Fig. 13.

In the drawings, the same reference numbers are applied to the same parts throughout the several views, and the sectional views are taken on the section lines looking in the direction of the arrows at the ends thereof.

Referring principally to Figs. 1 and 2, there is shown a pressure chamber 20 formed in a cylindrical pressure housing 2| made of tough metal, said housing 2| having a reinforcing sleeve 22 fitted snugly thereover to increase its strength. The pressure chamber 20 opens on the end 23 of the pressure housing, an enlarged portion of said opening being threaded as at 24 to receive the threaded coupling portion 25 of an explosion head 26 which has an explosion chamber 21 opening outwardly of said threaded portion 25, by which the explosion head may be coupled to the pressure housing. The extreme end of the coupling part of the explosion head is provided with a shoulder 28 which is screwed against a gas and uid sealing gasket 29 seated on shoulder 3D of the pressure housing to form a gasproof and waterproof seal. The explosion head 26 is also provided with a cylindrical snugly-fitting reinforcing sleeve 3Ia, adding to its strength.

The explosion chamber 21 is of cylindrical contour and is provided with a cylindrical piston 3| which is fitted into the cylinder and is used to coni-ine an explosive charge 32 therein. Explosion of this explosive charge 32 will drive the piston toward the pressure chamber 20 and exert pressure on the fluid 33, which may be water.

In assembling the device for an operation, the pressure housing is set on its end 34 and there is placed therein the article to be formed, encased in a rubber bag-like sheath, preferably evacuated of all air or gas. The explosion head with the powder charge 32 therein and the piston 3| compressed thereagainst is then screwed into the pressure housing 2|, by means of a tool inserted in holes 26a (Fig. 3), until the shoulder 28 seats firmly against the gasket 29 resting on gasket retaining shoulder 30. During this coupling of the explosion head to the pressure housing, the excess water will be expelled along the threads 24 until the final coupling and sealing of the two together occurs. In this way there will be no air or gas left in the pressure chamber 2|) which otherwise would tend to lessen the effect of the explosion which drives piston 3| against the fluid.

The ignition device for detonating the explosive contained in chamber 21 comprises a pair of electrodes 35 and 36 (see Figs. 1 and 7) having an electric match 36a in series therewith. A mushroom base 38, having a neck portion 39 is placed neck rst through a hole 40 bored through the end 4| of the explosion head, the enlarged base portion 38 being seated in an enlarged section 42 of bore 4 I, and is sealed therein by a gasket 43 against shoulder 44. Neck portion 40 has a threaded end extending beyond the end 4| of the explosion chamber and is engaged by a retaining nut 42 to hold the base 38 fixed within the section 42. Small holes 44a are provided in nut 42 for insertion of a tool to tighten it. Electrode 35 (Figs. '7, 13 and 14) extends through a hole 45 extending axially of neck portion 39 and through enlarged hole 46 in the explosion chamber end of the base 38. For that portion of the length of electrode 35 which is within the neck 39, it is covered by a dielectric sheath 46a to prevent short circuiting thereof. To make the assembly of the electrode 35 to base 38 pressure proof, a conical Washer 41 of hard resinous material, a washer 48 of gasket elastomer material, a washer 49 of hard resinous material, a washer 5 0 of gasket elastomer material, and a washer 5| of asbestos are held compressed by packing nut 52, screwed on electrode 35, which eifectually seals the electrode 35 to the base and prevents its blowing out and prevents blow-by of gases produced by reason of the explosion which it detonates. Electrode 36 is grounded in the enlarged portion 38 of the mushroom base which makes electrical contact with the explosion head. Referring to Fig. 7, the projecting threaded end of electrode 35 is provided with a nut 55 which can be tightened against dielectric washer 55a and by which an electrical conductor may be secured thereto. At the time detontion of the explosive is wanted, an electric circuit is completed to ignite'the electric match which includes a hot wire loop embedded in igniting powder contained in a small metal cylinder.

In order that the pressure built up in the explosion head chamber by detonation of the explosive may be dissipated at the conclusion of the compacting, so that the explosion head may be removed from the pressure housing, a relief valve has been provided, said valve being shown in detail in Figs. 9, 10, l1 and 12. The said relief valve is shown in Fig. 1 screwed into a threaded opening 60 bored in the end 4| of the explosion head.

Referring to the detailed showings of the relief valve in Figs. 9 to 12 inclusive, there is provided a valve body 6| externally threaded as at 62 so it may be screwed into the threaded bore 60 of the explosi-on chamber (see Fig. l), a shoulder 53 thereon abutting against a shoulder 64 (see Fig. 1) of the explosion head, with a gasket 65 positioned therebetween. Valve body 6| has an axial bore threaded as at 65a, to receive through opening 66 a needle valve element 61 pressure sealed by packing gland 68 and packing 69 held in place by packing nut 10 threadedly coupled onto the threaded end 1| of the valve body 6|. The inner end of the axial bore in the valve body is formed to a valve seat 12 leading to a very small passageway 13 opening onto the inner end 14 of the valve body. The needle valve element hasa needle point end 16 which enters the valve seat 12 when the needle valve element is screwed inwardly to its limit thereby blocking the passage of any gas or water through the small portion 13 of the axial bore of the valve body. The needle valve is flattened near end 16, as at 11, to give a clearance 18 to a port 19 leading to an axial bore 80 extending to the outer end opening 8l of the needle valve element 61, so that when saidneedle valve is screwed out of its seat, by lturning nut 83, the gases of explosion may escape by way of passageway 80 in a controlled manner. The end of the needle valve element 61, through which the gas escapes, may be stepped as at 82 so as to form a fitting to which a hose may be coupled so that the gases, which may be toxic or corrosive, may be conveyed to wherever it is convenient. Referring to Fig. 1, a small passageway 85 leads from the explosion chamber 21` to the bottom of the bore 60 wherein the valve body is inserted, so that when the needle valve 16 is screwed out of its seat there is a continuous small passageway for the passing oii of explosion gases.

In Figs. 1 and 2 there is shown, respectively, the condition of `the device before an explosion takes place and the condition of the same device after an explosion has taken place, and there is shown the effect of the explosion upon a cube-like form of article or powder compact encased in a rubber sheath from which excess air and gas has been previously removed. It will be seen that the article contained in the bag 86, as shown in Fig. l, is slightly larger in lineal dimensions than the same article, after the explosion, as shown in Fig. 2, the volumetric change being equal to the iluid displacement of that portion of the piston 3l which has entered the iluid chamber 20 at the -consummation of the explosion. The particular shape shown for the article under treatment was selected as a cube-like form for convenience only, it being understood that the article may be of any shape, and that it will be compacted /uniformly because of the equalizing hydraulic pressure. The amount of uid dis,- placement which the piston 3l has made in the pressure chamber is a measure of the compacting accomplished by the explosion. It should be understood that the article need not necessarily be in briquette form made by a iirst light compacting of the material, as loose metal powder itself may be placed within such bags and made to assume a conformation determined by the elastomeric properties of the bag, such conformation being retained and resulting in a coherent body upon an explosion taking place.

In using the process where a. number of objects are to be made alike, in a series of operations, it is desirable that the obtained results in each case be the same. To this end the initial dimensions, the degree of initial compacting, charge of powder and its density of loading should be the same for each operation.

The best range of pressure for molding hard carbide metal compounds, such as tungsten carbide, or mixed tungsten carbides and other carbides, is between 50,000 and 60,000 pounds per square inch, which requires from two to three grams of explosive powder per cubic centimeter of compacting of the article or articles, if ordinary single or double base smokeless powders of web size from .022 to .150 inch are used. Ordnance type powders of perforated grain formation are satisfactory for use in the device described above, but black powder will do.

It is desirable in the operation of this device that pressures be not developed too rapidly, the maximum pressure for best results should be developed within the range of 25 milliseconds to 50 milliseconds.

Certain dimensions for various parts of the device have proved to be satisfactory and will be given, but these are not to be deemed limiting the invention in any way, as wide differences in dimensions and even in form of construction may be tolerated. In a device as shown with a diameter of explosion chamber of three inches and an explosion chamber length of seven inches, a piston of six inches length and of a diameter giving a clearance of .0005 of an inch has proved satisfactory for use with a pressure chamber having a length of about thirteen inches and a cylindrical diameter of about 3% inches. I f, in a device of such dimensions, a tungsten carbide slug compacted toa handling condition, having an initial volume of 185 cubic centimeters, is nally compacted by the use of grams of single base smokeless powder with a web of .022 inch and loaded to a density between .70 and .90, the final volume of the slug Would be approximately 130 cubic centimeters, making the compression 55 cubic centimeters, or equivalent to about 2.4 grams of powder per cubic centimeter of cornpression. The pressure attained under such circumstances is about 51,000 pounds per square inch. The above example will give an idea of the compacting results to be expected.

In practice it is desirable to put the device in a heavy walled concrete pit with the ignition wires leading out to the operator who stands, protected, at a distance. The explosion gases, conveniently, may be released in approximately half a minute by opening the needle valve. If it proves to be desirable with any particular type of molding powder, an appreciable pressure could be maintained for a long period of time, depending upon the effectiveness of the sealing construction used.

It has been found that the density of the loading of the powder need not be ,more than .'10 to -.90, such figure representing the ratio between the weight of the explosive with which the charge is made and the weight of Water which would completely lll the same explosive occupied volume of the explosion chamber.

In carrying out the process, either the loose metal powder or a briquette compacted of it, under low pressure, to the contours of the desired shape, known as a powder compact, is placed in an elastomeric duid-resisting sheath of bag-like form, the air being exhausted from the bag as far as possible and the bag sealed, as by tying. The protected material is then placed in the pressure chamber and the pressure chamber is lled with water to the brim. Next the charged explosion head, with the piston packed againstthe powder in the powder end, is screwed into the pressure housing so that the piston bears against the water without the presence of any air or gas to lessen the ramming force of the piston as the explosion occurs. The explosion head and the pressure housing are coupled tightly together to maintain pressure. Next the explosive charge is ignited by completing an electric circuit through the electric match in the powder holding chamber, as by use of a battery connected on one side of the circuit to the central electrode and on the other side to within the device, even though the atmosphere or gas is otherwise excluded, so that the forcing of thepiston into the fluid and the fluid displacement will not cause the fluid to escape and allow the piston to travel through the uid to strike the included work therein.

It is obvious that the parts of the pressure housing and the explosion head and the various parts of the relief valve mechanism and ignition mechanism, and the piston, may be made from any strong metal, such as is used for ordnance, or other high pressure devices.

The combined use of fluid pressure media and an explosive force given to it, to compress the included work material, or powder compact which is protected from the iiuid, gives a very superior product where strength and density of the compacted article, and its freeness from porosity, is a desirable feature. The exceptionally dense and uniformly dense product obtained by this method increases not only the strength by making a uniform product without any strain or cracks therein, but makes the product have a greater strength because of better union of the particles.

It will be obvious that details of the process may be varied somewhat, without departing from the spirit of the invention and, therefore, the invention is claimed broadly.

Having thus described our invention what we claim as new and useful and desire to secure by Letters Patent is:

1. The improvement in the art of powder 8 metallurgy comprising the surrounding of a powder compact with a body of liquid and subjecting said body of liquid to explosive pressure transmitted thereby uniformly to said compact from all directions, to condense said compact uniformly.

2. The improvement in the art of powder metallurgy comprising the surrounding of a powder compact with a body of liquid and subjecting said body of liquid to pressure developed to a maximum within the range of 25 to 50 milliseconds, said pressure being transmitted by said liquid to the compact from all directions to condense said compact uniformly.

3. The process of claim 2 in which the powder compact is separated from the liquid by a pliable rubber envelope enclosing the compact.

PHILIP M. MCKENNA. JOHN C. REDMOND. EMLYN N. SMITH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 669,279 Harrington Mar. 5, 1901 1,081,618 Madden Dec. 16, 1913 1,338,676 Constantinesco May 4, 1920 1,371,671 Duryea et al. Mar. 15, 1921 '1,824,457 Barlow Sept. 22, 1931 1,891,234 Langenberg Dec. 20, 1932 2,177,044 Nardone Oct. 24, 1939 2,207,936 Nardone July 16, 1940 2,220,018 McKenna Oct. 29, 1940 2,299,464 Coffman Oct. 20, 1942 2,320,680 Temple June 1, 1943 2,309,978 Pratt Feb. 2, 1943 FOREIGN PATENTS Number Country Date 21,840 Great Britain Sept. 23, 1897 545,048 Great Britain May 8, '1942 548,727 Great Britain Oct. 22, 1942 

